This invention relates to a process for producing a vinylamine-vinyl alcohol copolymer, more particularly, a process for easily obtaining the copolymer in the form of powder, and uses of the copolymer as a hair setting composition or a hair conditioning composition.
Vinylamine-vinyl alcohol copolymers are known to have various functions. For example, JP-A-62-74902 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) describes the function as a chemical to be used in papermaking. U.S. Pat. No. 4,713,236 teaches application to hair care products including shampoos. JP-A-9-87144 discloses use in a hair conditioning composition. JP-A-9-87151 proposes use in hair styling cosmetics.
Although N-vinylformamide, which is a starting material of the vinylamine-vinyl alcohol copolymer, has recently come to be available in industry, the vinylamine-vinyl alcohol copolymer itself is not manufactured on an industrial scale for the time being because an economical process of production has not been established as yet.
Processes of producing the copolymer that have hitherto been reported include a process comprising acid-hydrolysis of an N-vinylformamide-vinyl acetate copolymer in water (see JP-A-62-74902) and a process comprising polymerizing N-vinylformamide and vinyl acetate in an alcohol followed by hydrolysis (see JP-B-6-51741; the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d). The former process yields the polymer in the form of an aqueous solution, which is inconvenient in transportation or purification. The latter process has an advantage of easy purification because the polymer is obtained in the form of powder but is disadvantageous in that, for one thing, a large quantity of an alcohol is required, which leads to an increase of cost, and, for another, complicated production steps are involved.
The present invention has been completed in the light of the above-described circumstances. An object of the present invention is to provide a vinylamine-vinyl alcohol copolymer in a powdered form at a low cost.
As a result of extensive studies, the present inventors have found that the vinylamine-vinyl alcohol copolymer precipitates in a powdered form where a copolymer comprising an N-vinylamide unit and a vinyl acetate unit as dispersed in water is hydrolyzed under a basic condition. Where the N-vinylamide-vinyl acetate copolymer is hydrolyzed in water in an acidic condition as in the known process, the vinylamine unit of the hydrolysate takes the form of a salt (e.g., a hydrochloride) so that the resulting polymer dissolves in water. On the other hand, where the hydrolysis is conducted under a basic condition according to the invention, the vinylamine unit takes the form of a free amine, and the desired polymer is salted out by the influence of hydrolysis by-produced salts such as sodium acetate and sodium formate.
The polymer obtained by hydrolysis under a basic condition unavoidably contains by-produced salts, such as sodium acetate and sodium formate. Washing with water is a conceivable method for removing these salts. However, the polymer, being water-soluble, will be dissolved when merely washed with water, resulting in a considerable washing loss, which eventually leads to an increase of the polymer price.
The present inventors have continued their study to settle the above problem of washing loss and, as a result, found a specific means for washing the hydrolysis reaction mixture which is obtained by hydrolyzing a copolymer comprising an N-vinylamide unit and a vinyl acetate unit under a basic condition to remove only the impurities without being accompanied by dissolution of the desired polymer.
The gist of the present invention consists in a process for producing a powdered water-soluble polymer comprising hydrolyzing a copolymer comprising an N-vinylamide unit and a vinyl acetate unit while dispersed in water under a basic condition and then washing the resulting powdered water-soluble polymer with at least one washing liquid selected from an alcohol, water at 20xc2x0 C. or lower, and salt water.
The polymer which can be used in the invention as a starting material is a copolymer mainly comprising an N-vinylamide unit and a vinyl acetate unit. The monomer providing the N-vinylamide unit includes N-vinylformamide and N-vinylacetamide, with N-vinylformamide being preferred. The starting copolymer usually comprises about 1 to 50 mol % of the N-vinylamide unit and about 50 to 99 mol % of the vinyl acetate unit.
The molar ratio of the N-vinylamide unit and the vinyl acetate unit in the copolymer usually ranges from 1:99 to 50:50, preferably 5:95 to 50:50. Where the N-vinylamide unit content is too high, the hydrolyzed polymer tends to dissolve.
The starting copolymer may further comprise other arbitrary monomer units as long as the desired characteristics of the resulting polymer are not impaired. The content of the other monomer units, while varying depending on the monomer, is usually 30 mol % or less based on the total monomer units.
The N-vinylamide-vinyl acetate copolymer can be prepared by known techniques such as emulsion polymerization or suspension polymerization in water. Emulsion polymerization is recommended for ease in handling the resulting polymer. Polymerization is carried out by radical polymerization preferably in the presence of an azo initiator. The monomer concentration in the polymerization system is usually 1 to 50% by weight, preferably 10 to 45% by weight. If desired, assistants, such as an emulsifying agent used in emulsion polymerization or a chain transfer agent as a molecular weight modifier, can be used. The reaction mixture as obtained by emulsion polymerization or suspension polymerization is a white emulsion or a slurry, respectively.
The polymerization is followed by hydrolysis. The polymerization reaction mixture (e.g., an emulsion or a slurry) can be subjected to hydrolysis as such or, if desired, with the polymer concentration in water adjusted by dilution with water or concentration by, for example, evaporation of water. The concentration of the polymer to be hydrolyzed is usually in the range of 1 to 50% by weight, preferably 10 to 45% by weight. If the polymer concentration is too low, the hydrolysate polymer may dissolve. Too high a polymer concentration requires much power for stirring.
The hydrolysis should be carried out under a basic condition. The basic condition is preferably such as created in the presence of a strong alkali, particularly a caustic alkali such as caustic soda or caustic potash.
The alkali is usually added in an amount of 0.1 to 10 equivalents, preferably 0.5 to 5 equivalents, per equivalent of the total monomers. It should be noted that the polymer after hydrolysis is water-soluble. It is the salt by-produced by the hydrolysis that causes the water-soluble polymer to precipitate. Therefore, where the amount of the base is small, and the degree of hydrolysis is low or where the reaction system has a low concentration or in like situations, the salt concentration may be so low that the polymer easily dissolves or swells, resulting in a filtration failure. Such a case can be managed by adding a supplementary salt to accelerate precipitation (salting-out) of the polymer. Salts which can be added include sodium acetate, potassium acetate, sodium formate, potassium formate, sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, calcium chloride, sodium carbonate, and potassium carbonate. In particular, addition of a salt of a polybasic acid, such as sulfuric acid, phosphoric acid or carbonic acid, is effective in precipitating the polymer. The salt concentration in the precipitation system, i.e., the total of the salt by-produced by the hydrolysis and the supplementary salt added to accelerate salting-out, is usually 0.5 to 50% by weight, preferably 1 to 30% by weight. The supplementary salt, if needed, is preferably added after completion of the hydrolysis rather than before hydrolysis.
In order to increase the degree of hydrolysis and to prevent the hydrolysate polymer from sedimentation in lumps, it is preferred that the reaction mixture be stirred strongly during hydrolysis. The hydrolysis reaction temperature is usually about 20 to 100xc2x0 C. While not limiting, the hydrolysis reaction time is usually about 10 minutes to about 10 hours. The degree of hydrolysis of the polymer is usually 10 to 100%, preferably 20 to 100%, as for both the N-vinylamide unit and the vinyl acetate unit. It is acceptable to increase the hydrolysis degree of only the vinyl acetate unit by, for example, temperature adjustment.
By the end of the hydrolysis, the reaction mixture has become a slurry, which is usually cooled and separated into solid and liquid by filtration, centrifugation, sedimentation or a like means to collect the solid matter. Since the by-produced acetate and formate are water-soluble, most of impurities other than those present in the surface water on the collected solid can be removed by the solid-liquid separation, provided that the supplementary salt or assistants to be added in the preceding steps are selected from water-soluble ones.
Subsequently the collected polymer is washed to remove the impurities incorporated into the polymer. The polymer being water-soluble, washing with water will remove the impurities but is accompanied with a considerable loss of the polymer. In the present invention, washing is effected with a washing liquid comprising at least one member selected from (1) an alcohol, (2) cold water at 20xc2x0 C. or lower, and (3) salt water in order to remove the impurities in the polymer with a minimized polymer loss.
In case of using an alcohol, alcohol-soluble salts can be washed away while the polymer remains undissolved. The alcohols which can be used suitably include lower aliphatic alcohols having 1 to 4 carbon atoms, such as ethanol, methanol, and isopropyl alcohol. Washing with these lower alcohols easily achieves purification, removing such salts as sodium formate by dissolution. The merit of using an alcohol resides in the possibility that some of the emulsifying agents that may have been used in the polymerization can be washed away efficiently. The alcohol for washing is usually used at a temperature of 40xc2x0 C. or lower, preferably 30xc2x0 C. or lower. In using an alcohol as a washing liquid, it is preferred that the salt to be supplementarily added for salting-out in the preceding stage be selected from those having high solubility in the alcohol.
In case of using cold water as a washing liquid, water-soluble impurities can be washed off while virtually suppressing dissolution loss of the polymer. Since the solubility or the rate of dissolution of the polymer in water increases with temperature, the temperature of the washing water should be 20xc2x0 C. or lower, preferably 10xc2x0 C. or lower, still preferably 0 to 5xc2x0 C.
Where the polymer is washed with salt water, impurities other than the salt of the salt water, such as sodium formate and sodium acetate, can be removed. Suitable salts of salt water include sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, and calcium chloride.
While somewhat varying depending on the kind of the salt, the salt concentration in the salt water is usually 0.5% by weight or more, preferably 1% by weight or more, still preferably 3% by weight or more. The temperature of the salt water is usually 40xc2x0 C. or lower, preferably 30xc2x0 C. or lower.
The washing method using cold water or salt water is economically advantageous because no solvent other than water is used.
The washing liquid may be a mixture of two or more of the alcohol, cold water (20xc2x0 C. or lower), and the salt water. For example, a mixture of an alcohol and water in a mixing ratio of 1:10 to 10:1 by volume can be used at a liquid temperature of 30xc2x0 C. or lower, preferably 20xc2x0 C. or lower.
Washing can be performed by sedimentation followed by decantation, filtration followed by washing and rinsing and the like. The number of washing times can be decided arbitrarily. Washing with a washing liquid of a kind (an alcohol, cold water, salt water or a mixture thereof) or a combination of two or more kinds can be repeated several times. Washing is usually conducted until the total concentration of the acetate and the formate by-produced by the hydrolysis in the polymer is reduced to 5000 ppm or less. The by-produced acetate and formate include sodium acetate, potassium acetate, sodium formate and potassium formate.
The washed polymer is dried in a conventional manner, for example, by air blowing or vacuum drying. Drying temperature is preferably 100xc2x0 C. or lower, still preferably 60xc2x0 C. or lower. The resulting powdered polymer, which is water-soluble, is re-dissolved in water, preferably warm water, on use. It is recommended to use warm water at 40 to 100xc2x0 C.
The water-soluble polymer produced by the above-described process can be used as, for example, wet-end paper additives, dry-end paper additives, a dispersant, coatings applied to paper or a plastic film, and hair care products such as a shampoo. The polymer exhibits the respective desired functions in these uses. When used as a coating of a plastic film, etc., the polymer has a sufficiently low content of impurities and undergoes no reduction of transparency or color change. The water-soluble polymer of the invention is particularly suited as a component of hair care products, providing hair-setting compositions including hair sprays, styling gels, and styling mousses; shampoo compositions; hair conditioning compositions including hair conditioners and treating formulae for damaged hair, and the like. Form of these hair care products include a lotion, an emulsion, gel, foam, and aerosol. The hair-setting compositions comprising the water-soluble polymer of the invention have excellent and long-lasting hair-setting performance (ability to maintain hair in a desired style). The hair conditioning compositions comprising the water-soluble polymer of the invention exhibit excellent moisture retaining effects.
In addition, the water-soluble polymer of the invention can be used as a dye fixing agent, a kind of dyeing auxiliaries. It is especially effective on dye fixing of cotton fiber dyed with reactive dyes. The polymer also exhibits marked effects as an ink fixing agent which is applied to the acceptor for ink jet printing, such as paper, films, fabric, etc. In connection with dyeing of fiber, the polymer is also suitable as an assistant ink jet dyeing.
The present invention will now be illustrated in greater detail with reference to Examples, but it should be understood that the invention is not construed as being limited thereto. Unless otherwise noted, all the percents are by weight.